AP Bio Cell Communication

what is Homeostasis

• Steady state or internal balance

• Cells maintain a relatively constant internal environment even when the external environment changes significantly

set point def

The internal condition’s typical state

stimulus def

Fluctuations in that condition above or below the set point`

sensor function in homeostasis

• A receptor or sensor detects the stimulus and triggers a response, an activity that returns the condition to the set point

negative feedback

response reduces the stimulus; brings the body closer to set point

positive feedback

stimulus is amplified in order to complete a process then the condition returns to the set point; moving away from set point

Autocrine signaling

a cell send a signal to itself

Juxtacrine signaling 

cells communicate with adjacent cells through direct contact

paracrine signaling

cells communicate to nearby cells by releasing chemical messengers 

Endocrine signaling

cells communicate to cells far away by releasing chemical messengers that are carried to the target cell

Three steps of signal transduction pathway

1) Reception

2) Transduction

3) Response

ligand

signal molecule

Reception

ligand bonds to a receptor protein in a lock and key fashion (highly speficic) causing te receptor to change shape

What receptor proteins do hydrophilic ligands bind to

plasma membrane receptors (can’t pass through membrane)

what receptor proteins do hydrophobic/small ligands bind to

intracellular receptors (can pass through membrane) 

G- Protein Coupled Receptors - what does it bind to

G-protein binds to GTP (like ATP)

G- Protein Coupled Receptors - relative sturcutre

all very similar

G- Protein Coupled Receptor system - relative function

extremely widespread and diverse 

Receptor Tyrosine Kinases - what are they

RTKs are membrane receptors that transfer phosphate groups from ATP to another protein

Receptor Tyrosine Kinases - amount of pathways triggered

multiple at once

Ion Channel Receptors - what does it act like

a gate that opens and closes when the receptor changes shape

Ion Channel Receptors - how does it work

when a signal molecule bongs as a ligand to the receptor the gate allows specific ions, such as Na+ or Ca+2, through a channel in the receptor

Transduction - function

• molecular interactions relay signals from receptors to target molecules in the cell

• at each step in a pathway the signal is transduced into a different form, commonly a conformational change in a protein

Transduction. - pathway

multistep pathways

• Can amplify a signal (by activating multiple copies of the next component in the pathway)

• Provide more opportunities for coordination and regulation 

Transduction - Phosphorylation

• in this process, a series of protein kinases add a phosphate to the next one in line, activating it

• phosphate enzymes then remove the phosphates

Transduction - secondary messengers (what are they)

secondary messengers are small molecules/ ions that relay signals received by receptors to proteins

Transduction - Common secondary messengers

• Cyclic AMP (cAMP)

• Calcium

  • concentration of cytosol is much lower than outside the cell meaning a small change in the number of calcium ions represents a large percentage change in calcium concentration

Transduction - Scaffolding Proteins

scaffolding proteins can increase the signal transduction efficiency

Response - possible responses (4)

• same signal molecule can trigger different responses

• many responses can come from one signal

• signal can trigger an activator or an inhibitor 

• signal can trigger multiple receptors and different responses

How to stop the Response

signal response is terminated quickly when the ligand detaches from the receptor

What is cross talk

the interaction between different signal pathways within a cell where one pathway influences the other

• ex. activator made from one signal pathway goes and activates a relay molecule of another pathway